The scope and nature of hostile military activities, such as battles, firefights and pre-battle reconnaissance, have changed markedly with the introduction of portable, heavy duty weapons and special armor and increased incidences of urban warfare. The typical mobile warrior now is heavily armed, is still quite mobile, and is less vulnerable to small arms tire. The armored tank personnel carrier or tank is heavily protected and must receive a near direct hit to be seriously disabled. This requires fire control that receives very accurate location coordinates for its targets. For battles fought on an open field, and for firefights in an urban warfare situation, this requires determination of the target coordinates by an observer, using equipment that is portable and that provides readings accurate to within a few meters.
In another class of hostile environments, the location of a fire or of a toxic chemical spill that cannot be approached within a reasonable distance is sought, with an associated inaccuracy of less than a few meters.
Several location determination systems are available for such measurements, based on signals received from satellite sources or from ground-based sources. However, many of these systems have associated inaccuracies that are much larger than a few meters. Two location determination systems that may provide the needed location accuracies are the Global Positioning System (GPS) and the Global Orbiting Navigational Statellite System (GLONASS). In particular, GPS techniques have recently been applied in mapping and survey activities where location coordinates are sought.
Deem et al. in U.S. Pat. No. 4,384,293, disclose use of two or more GPS signal antennas, arranged in a line, to obtain information on the angular orientation of that line in a given plane. The radiating elements of adjacent antennas on the line are spaced apart by a fixed multiple of the GPS signal wavelength used.
U.S. Pat. No. 4,807,131, issued to Clegg, discloses an automated land grading system in which the position of a cutting blade is controlled automatically to provide controlled shaping of a land region being graded. A laser beam is projected in a predetermined pattern across the land region, and a laser detector carried on the grading machine receives the beam and approximately determines the location of the cutting blade and the blade angle and depth appropriate for grading that location in the land region. Information on the desired blade angle and depth is stored a microprocessor carried on the grading machine and is compared with the actual blade angle and depth to correct the blade orientation and elevation.
Paramythioti et al, in U.S. Pat. No. 4,873,449, disclose method and apparatus for three-dimensional surveying, using triangulation and a laser beam that propagate along the perimeter of a triangle. A rotatable mirror, a component of the scene to be surveyed, and a light-sensing means are located at the three vertices of the triangle, and knowledge of the angles of orientation of the rotatable mirror and the camera allow determination of the location of the component of the scene presently being surveyed. Three fixed, spaced apart stations, including one station at the scene to be surveyed, and receipt of a line-of-slight light beam are required here.
Apparatus for determining compass headings, using two GPS antennas located at fixed positions aboard a ship or aircraft, is disclosed in U.S. Pat. No. No. 4,881,080, issued to Jablonski. The absolute positions of the GPS antennas must be determined with the usual inaccuracies. A GPS receiver/processor receives the signals sensed by the GPS antennas and determines a compass heading of the ship or aircraft, based upon the known relative positions of the two antennas on the ship or aircraft. A similar configuration, applied to mapping of ocean currents from an aircraft, is disclosed by Young in U.S. Pat. No. 4,990,922.
Gaer, in U.S. Pat. No. 4,924,448, discloses survey apparatus and method for mapping a portion of an ocean bottom. Two ships, each equipped with identical GPS signal antennas, receivers and processors, move along two parallel routes a fixed distance apart on the surface of an ocean. Each ship takes radio soundings of a small region of the ocean bottom directly beneath itself and receives a reflected radio sound from that same region that is originally transmitted by the other ship. The depths of the region directly beneath each ship, as determined by each of the two radio sound waveforms and by the GPS-determined locations of the two ships, are determined and compared for purposes of calibration. A related invention is disclosed by Gaer in U.S. Pat. No. 5,231,609.
A mobile target indicator system, for use in a battlefield, is disclosed by Ruszkowski in U.S. Pat. No. 4,949,089. The target locator system includes GPS antenna and receiver/processor, a radio transmitter, a laser rangefinder, azimuth angle sensor and elevation sensor. A rifleman carries the system into the battlefield and directs the laser rangefinder at a target. The radio transmitter transmits the rifleman's GPS-determined location and the offset location of the target relative to the rifleman to another entity, such as a weapons delivery system to be used against the target. However, in a cluttered battlefield, the operator of the weapons delivery system, and even the rifleman, cannot be certain that the correct target is being sighted.
In U.S. Pat. No. 4,954,833, issued to Evans et al, a method is disclosed for determining the location of a selected and fixed target or site, using a combination of GPS signals and the local direction of gravitational force. Geodetic azimuth is determined using GPS signals, and the local gravitational force vector is used to relate this location to an astronomy azimuth, using a fixed coordinate system that is independent of the local coordinate system. The target and a reference site are each provided with a GPS signal antenna, receiver and processor to determine the local geodetic azimuth.
Evans, in U.S. Pat. No. 5,030,957, discloses a method for simultaneously measuring orthometric and geometric heights of a site on the Earth's surface. Two or more leveling rods held at fixed, spaced apart locations, with a known baseline vector between the rods. Each rod holds a GPS signal antenna, receiver and processor that determines a GPS location for each rod. The geometric height of the GPS antenna (or of the intersection of the rod with the Earth's surface) is determined for each rod, and the geometric height difference is determined, using standard GPS measurements (accurate to within a few meters). The orthometric height difference for each GPS antenna is determined using the measured GPS location of each rod and an ellipsoid or geoid that approximates the local shape of the Earth's surface.
Use of three or more GPS antennas, arranged in a collinear or non-collinear array on a body, to determine the attitude or angular position of the body, is disclosed by Hwang in U.S. Pat. No. 5,021,792 and by Timothy in U.S. Pat. No. 5,101,356. The antennas in the Hwang patent can be rearranged into collinear or non-collinear patterns, and GPS signal measurements are taken before and after rearrangement to determine the angles describing arrival of the GPS signals. In the Timothy patent, three antennas are spaced apart at calibrated distances in a selected pattern, possibly collinearly. The phase differences of each GPS signal arriving at a pair of these antennas are used to determine the angle of arrival of that GPS signal. A similar system, using two spaced apart GPS signal antennas, is disclosed in U.S. Pat. No. 5,119,103, issued to Evans et al.
A surveying instrument that uses GPS measurements for determining location of a terrestrial site that is not necessarily within a line-of-sight of the surveyor is disclosed in U.S. Pat. No. 5,077,557 issued to Ingensand. The instrument uses a GPS signal antenna, receiver and processor, combined with a conventional electro-optical or ultrasonic range finder and a local magnetic field vector sensor, at the surveyor's location. The range finder is used to determine the distance to a selected mark that is provided with a signal reflector to return a signal issued by the range finder to the range finder. The magnetic field vector sensor is apparently used to help determine the surveyor's location and to determine the angle of inclination from the surveyor's location to the selected mark. A second patent issued to Ingensand, U.S. Pat. No. 5,233,357, discloses a "total" surveying station that uses a GPS reference receiver, electrooptical measuring equipment, and a electromagnetic signal roving receiver to determine the roving receiver location and separation vector joining the reference and roving receivers.
In U.S. Pat. No. 5,146,231, Ghaem et al disclose an electronic direction finder that avoids reliance on sensing of terrestrial magnetic fields. The apparatus uses a directional antenna and receiver/processor, for GPS or similar navigation signals received from a GPS satellite, and requires (stored) knowledge of the present location of at least one reference GPS satellite from which signals are received. The orientation of the finder or its housing relative to a line of sight vector from the finder to this reference satellite is determined. This orientation is visually displayed as a projection on a horizontal plane. Any other direction in this horizontal plane can then be determined with reference to this projection from a knowledge of the reference satellite location.
A multiple GPS antenna system for antenna pointing or three-dimensional attitude measurement is disclosed by Ward et al in U.S. Pat. No. 5,185,610. At least two spaced apart antennas are used for pointing, and at least three spaced apart, non-collinear antennas are used, with the distances of separation being much less than the correlation distance for the GPS signals used (29.3 meters and 293 meters for P-code and C/A-code, respectively). Inclusion of more than the minimum number of GPS antennas needed for the application allows optimization of the overdetermined GPS solutions. In-phase and quadrature signals are generated and analyzed by the system.
U.S. Pat. No. 5,193,064, issued to Maki, discloses a system for integrating GPS signals and inertial navigation system (INS) signals, without using accelerometers, to provide velocity steering and location information for an airborne vessel. Gyro readout signals provide information on the present direction of motion of the vessel.
Shaw et al disclose a system for measuring angles-of-arrival of radiowaves at a high performance, high maneuverability aircraft, using Doppler shifts of the waves and location and velocity vectors determined by an on-board GPS or INS, in U.S. Pat. No. 5,241,313. The aircraft velocity vector is changed in a preselected, segmented manner, and the corresponding Doppler shifts for each segment am analyzed to determine the propagation direction of the wavefronts.
Some workers have reconfigured camera viewfinders or similar apparati to attempt to measure distance of an object shown in the viewfinder. In U.S. Pat. No. 3,486,432, Norwood discloses a viewfinder for a conventional camera in which the present lens focal length used and the distance to a designated object are displayed along first and second orthogonal coordinate axes immediately adjacent to the standard viewfinder. The lens used here is an electronically operated zoom lens. Two levers adjust the focal length and focus distance of the zoom lens and, simultaneously, provide the focal length and distance parameter values displayed on the first and second coordinate axes. These parameter values are sensed and adjusted by portions of the light beam that forms an image for the film in the conventional camera.
Grassl discloses a single lens reflex camera having an optoelectronic distance meter mounted adjacent to the camera viewfinder. Two small portions of the image-forming light beam are split off and used to determine the distance to a designated object in the field of view of the camera lens. These small light beam portions are sensed by two light beam sensors that determine the lens-object distance by correlation of certain displaced images.
Corby, in U.S. Pat. No. 4,687,326, discloses a camera that integrates sensing of distance to each of a designated sequence of objects in the camera field of view and general luminance of the scene in the field of view. The designated objects are determined by a linear array decomposition (N.times.1) of a portion of the field of view, where the N objects in the linear array are interrogated by a time-and-space-coded sequence of light rays that scan across this linear array in the field of view. Sensing of the general luminance of the scene occurs during an (N+1)th member of this sequence in time so that a total of N+1 temporal slots are used to provide N lens-to-object distances and general luminance for the image in the field of view.
Neely discloses apparatus for sensing and displaying the distance from camera lens to designated object in the field of view in alphanumeric form in U.S. Pat. No. 4,754,296. Lens-to-object distance is sensed by a sonar echo technique that resembles radar. This apparatus also displays general scene brightness for the field of view. Lens-to-object distance and scene brightness are displayed alphanumerically in the viewfinder of the camera, which is preferably a single lens reflex.
Ozeki et al, in U.S. Pat. No. 4,961,155, disclose an XYZ coordinates measuring system that uses a television cronera with a slit light beam to generate signals, that determine a vector distance (.DELTA.x, .DELTA.y, .DELTA.z) from the lens to a a point on a work surface in the field of view.
A system mounted in a helmet for location determination is disclosed by Mocker et al in U.S. Pat. No. 5,208,641. The helmet includes light retroreflectors, such as cube comers or grooves, that reflect a plurality of beams of laser light directed toward the helmet. The helmet is intended to be used in an aircraft cockpit and typically will not move more than 60 cm in any direction. The time required for return of the light beams is processed to determine the helmet location.
In U.S. Pat. No. 5,216,480, Kaneko et al disclose a surveying instrument for measuring distance to, and azimuth of, a designated object. The instrument directs a light beam along an optical to the object, and the (small) deviation of the object from its customary location is measured using the return light beam. The object must strongly reflect the laser light.
Most of the measurement apparati used in these applications have many major measuring devices and are not portable, and none provides the observer with both an image of the target or other object and the location coordinates for that object. What is needed is a system that (1) provides very accurate location coordinates of the target, (2) provides an image of the target on which the coordinates are superimposed so that the correct target can be identified, (3) uses a small number of different measurement components, (4) provides means for backup in case a component is disabled or unavailable, (5) provides means for optimization of the target location coordinates determined by the system, (6) is portable, and (7) can be used anywhere on the Earth's surface.